[PATCH] D34176: [cmake] Make sure that -Wcast-qual is not a error in preparation for clang's -Wcast-qual for C++

[Justin Bogner via llvm-commits]

Roman Lebedev via Phabricator <reviews at reviews.llvm.org> writes:
> lebedev.ri created this revision.
> Herald added a subscriber: mgorny.
>
> Diagnostic `-Wcast-qual` is not enabled by default in gcc/clang, It
> was enabled explicitly some time ago.
> Later, clang has learned to do `-Wcast-qual`, like gcc does.
> While that clang diagnostic is compatible with gcc's, it additionally
> catches one more case, see https://reviews.llvm.org/D34153.
> And last but not least, clang's diagnostic `-Wcast-qual` only works
> for `C` code (sic!)
> In https://reviews.llvm.org/D33102, i have extended it to work for
> `C++` code too.
> Once that landed, `-Werror` buildbots broke. That is when i was made
> aware that this diagnostic is enabled in llvm builds.
> I have fixed that particular buildbot-discovered failure in
> https://reviews.llvm.org/D34153.
> However, when i tried building clang stage2 with self-built clang
> stage1 (with https://reviews.llvm.org/D33102), i have quickly
> discovered that some sub-projects also exhibit this warning.
> Specifically, **openmp** and **libcxx** subprojects produce **401**
> -Wcast-qual warnings, and i //believe// not all of these warnings are
> clang-specific.
> (i don't think i have all subprojects checked-out, so there may be even more)
> This tells two things:
>
> - these subprojects are not being built by `-Werror` buildbots. (at
> least as part of LLVM, not standalone)
> - no one builds LLVM by GCC with these subprojects with `-Werror` enabled.
>
> So, if https://reviews.llvm.org/D33102 is to land, this //may// not
> break `-Werror` buildbots. This is bad and good.
> But. If someone wants to build LLVM with these subprojects and with
> `-Werror`, he/she/it will face a lot of fatal warnings.
> It is unfeasible for me to fix all these warnings before re-landing
> https://reviews.llvm.org/D33102, thus i propose this diff.
>
> After https://reviews.llvm.org/D33102 has landed, the buildbots should
> //probably// be adjusted to catch these cases, and i will see if i can
> help fix these issues and revert this patch.
>
> Thoughts?

I'd rather we only set this to -Wno-error for the projects that actually
have this warning, and we leave it as is for the projects that are
already clean.

> Repository:
>   rL LLVM
>
> https://reviews.llvm.org/D34176
>
> Files:
>   cmake/modules/HandleLLVMOptions.cmake
>
> Index: cmake/modules/HandleLLVMOptions.cmake
> ===================================================================
> --- cmake/modules/HandleLLVMOptions.cmake
> +++ cmake/modules/HandleLLVMOptions.cmake
> @@ -521,6 +521,7 @@
>  if (LLVM_ENABLE_WARNINGS AND (LLVM_COMPILER_IS_GCC_COMPATIBLE OR CLANG_CL))
>    append("-Wall -W -Wno-unused-parameter -Wwrite-strings" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
>    append("-Wcast-qual" CMAKE_CXX_FLAGS)
> +  append("-Wno-error=cast-qual" CMAKE_CXX_FLAGS)
>  
>    # Turn off missing field initializer warnings for gcc to avoid noise from
>    # false positives with empty {}. Turn them on otherwise (they're off by